1. Field of the Invention
The present invention relates to a syringe and more particularly concerns a two-component medication syringe.
2. Description of the Prior Art
Some injectable medications have rapid loss of potency when they are in their ready-to-use form. In order to protect against the short shelf life of these medications, many of them are supplied in two components, and they are mixed at the time of use. Two-component medication is commonly available in two vials with pierceable stoppers. A first vial typically contains sterile water and the second vial contains the active ingredients which may be in lyophilized form. To prepare the medication for use, the user pierces the stopper of the vial containing the water with a sterile syringe and needle assembly and withdraws the water into the syringe. The needle is then removed from the first vial and inserted into the second vial. Water is injected into this vial to mix with the lyophilized medication. The mixed medication is then withdrawn into the syringe for injection. When the injection is to be made into a vein, it is common practice to insert the needle into the patient and to withdraw the plunger rod slightly from the syringe barrel. If the needle is in a vein, a slight amount of blood will be drawn into the syringe. The visual sighting of the blood verifies that the needle is in a vein. This procedure is called the vein indication test. Also, when injection of medication into a vein or artery is not desirable, the vein indication test can be used to assure that the hypodermic needle is not in a vein or artery.
The above recited known components present problems with respect to sterility since only the interior of the medication vial is sterile and bacteria from the exterior of the vials and the environment may be introduced into the medication during the mixing procedure. Also, at the areas where the cylindrical surfaces of the lumen of the hypodermic needle intersect the planes of its ground point, there are formed sharp edges that can potentially cut pieces of the rubber vial stopper away as the needle penetrates therein. These pieces of rubber represent a potential problem if they pass along with the liquid medication into the patient's body. Further, cost is high since two separate sterile containers and a sterile syringe are normally required.
Brown (U.S. Pat. No. 2,607,344) teaches placing both components of the medication in a glass tube where the components are separated by a stopper with a piston stopper sealing the end of the tube containing a liquid component and a flanged pierceable stopper sealing the end of the tube containing a powder component. Also, within the powder containing compartment, bounded by the stopper and the pierceable stopper, there is a longitudinally positioned groove projecting radially outwardly enlarging the inside diameter of the glass tubing. The groove is longer than the stopper so that when the stopper is positioned within the section of the tube containing the groove, liquid can flow around the stopper through the groove. Also provided is a separate barrel having an open proximal end adapted to accept the glass tube assembly and a distal end with a wall containing a cannula with opposed points. One end of the cannula projects into the barrel, and the other end projects outwardly away from the distal end of the barrel. In use, the tube assembly is inserted into the barrel so that the portion of the cannula inside the barrel penetrates the pierceable stopper establishing fluid communication between the interior of the tube and the atmosphere. Then the piston stopper is forced inwardly pushing the liquid component of the medication and the stopper toward the distal end of the barrel. When the stopper is positioned within the bypass, the liquid component flows around the stopper through the bypass to mix with the powder component. To perform the vein indication test, the tube is withdrawn to terminate fluid communication with the cannula and then the outwardly facing portion of the cannula is inserted into the patient. Since the flange of the pierceable stopper is larger than the inside diameter of the barrel, further withdrawal of the tube from the barrel creates a reduced pressure zone between the exterior end of the pierceable stopper and the cannula causing blood to flow from the cannula into the barrel, outside of the tube assembly, if the cannula is lodged in a vein.
Genese, in U.S. Pat. No. 4,226,236, teaches placing a liquid diluent and a solid medicament in a syringe barrel wherein the liquid diluent is contained between two stoppers and the solid medication is contained between one of the aforementioned stoppers and a hydrophobic filter which Genese suggests will not allow liquid to pass therethrough. This syringe contains an outwardly projecting bypass on the side of the barrel. To mix the medicament and the diluent the user removes a ferrule and the closure cap on the distal end of the syringe assembly and then pushes the plunger rod, which is attached to the first stopper, inwardly. The movement of the first stopper forces the diluent and the intermediate stopper in a forward direction until the intermediate stopper is positioned in the area of the bypass, and the diluent is then forced around the intermediate stopper through the bypass and onto the solid medicament. It appears that when the diluent contacts the entire surface of the hydrophobic filter, no air or water is permitted to pass and, further, that whatever air remains in the syringe after the diluent contacts the hydrophobic filter is trapped within the syringe and cannot escape.
At this point, Genese teaches that the syringe is to be shaken to cause mixing of the two components. To use this syringe, a slidably mounted hollow piercing member is moved rearwardly to puncture the hydrophobic filter and to allow fluid communication between the interior of the syringe barrel and the interior of the hollow piercing member. The distal end of the slidable piercing member is shaped to allow attachment of a hypodermic needle assembly. With the hypodermic needle assembly attached, the remaining air and mixed medication can be expelled from the syringe.
Brown, in U.S. Pat. No. 2,717,601 teaches an ampule for use as part of a hypodermic syringe. The ampule includes a tubular ampule body with its proximal end closed by a piston-type stopper and its distal end closed by a stopper. Between the ends of the ampule body a pair of axially extending grooves is formed in the wall thereof. A floating partition stopper is contained within the bore of the ampule on the proximal side of the grooves. A quantity of liquid diluent is contained in a first compartment which is defined by the space in the tube between the piston-type stopper and the floating partition stopper. A dry medication is contained in a second compartment which is defined by the space between the floating partition stopper and the stopper. In use, the piston-type stopper is driven along the ampule to force the floating partition stopper into the area of the grooves so the liquid diluent can pass around the floating partition stopper into the second compartment to mix with the dry medicament.
Bypass-type syringes, as taught in the patents alluded to hereinabove, require the movement of a partition stopper into a bypass area, wherein a liquid component is forced by a piston stopper around the intermediate partition stopper into the forward compartment for mixing. After all of the liquid is transferred the partition stopper and the piston stopper are in contact. When the medication is finally administered the operator forces the piston stopper and the partition stopper through the area of the bypass toward the distal end of the syringe. As the partition stopper and the piston stopper pass through the bypass area there is a tendency for medication trapped in the bypass and in the spaces between the piston stopper ribs and the inside of the syringe barrel to be projected in a rearward or proximal direction toward the operator's hands and/or the syringe plunger rod. This tendency is undesirable because some medications contain spores and/or active ingredients which should not be deposited on or near the operator's hands. Also, the presence of this liquid medication is at least a nuisance compromising the cleanliness of the injection process. The tendency to propel portions of the liquid medication in a distal direction will be called "blow-back" hereinafter.
Apparatus and methods for storage, mixing and administering two-component medication have been addressed by the prior art, as alluded to above. However, there is still a need for simple, straight-forward, reliable, easily fabricated syringe assembly for storage, mixing and administering of two-component medications. It is desirable that the syringe assembly minimize contamination potential by allowing the mixing and administering steps to be performed without puncturing stoppers or other barriers within the syringe or transferring the medication components through non-sterile barriers which are exterior to the syringe assembly. It is desirable that the syringe assembly be capable of easily performing the vein indication test and that it includes structure to block or prevent medication from being discharged through the proximal end of the syringe barrel during the injection process.